Method of lapping gear sets



P 1932- Y J. M. CHRISTMAN 1,879,089

METHOD OF LAPPING GEAR SETS,

Filed Feb. 21, 1931 [1 [WT/5. 1m

Patented Sept. 27, 1932 UNITED STATES PATENT OFFICE 2 JOHN--H. CHRISTIAN, OI DETROIT, MICHIGAN, ASSIGNOB TO PACKARD HOTOR CAB COMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN METHOD LAPPING GEAR SETS Application filed February 21, 1931. Serial N0. 517,519.

This invention relates to the finishing of gears and more particularly to methods for lapping gear sets.

'In the present method employed for lapping hardened steel gear sets, a pair of gears are first selected which mate and then run together with an intermittent application of an abrasive fluid compound. Due to the hardness of the gear material and the relation of the abrasive with the teeth tending to move from between the teeth, considerable time is required for the required lapping. Furthermore, when the gears of the sets are difierent sizes, for example a ring gear and pinion, the pinion will be ground faster than the ring gear which often results in undue lapping and in some instances, such as with hypoi gears, the faces of the pinion teeth are not uniformly finished and the finished portion ground too much. An object of this invention resides in a new and .improved method of lapping hardened steel gearsets which requires considerably less time than the methods now being em- .ployed. Y

Another object of the invention is to provide a method of lapping gear sets, in which the gears have a different number of teeth, so that the gear with the least number of wise and with a minimum removal of metal.

Other objects of the invention will appear from the following description taken in connection with the drawing, which form a part of this specification, and in which: Fig. 1 is an elevational view of a gear set, with the ring gear in section, associated in relation for lapping in, accordance with my invention;

Fig. 2 is a plan view of the same; Fig. 3 is a sectional view of the pinion coated with copper for the first lapping operation.

Referring now to the drawing, I have illus- 50 trated a hypoid gear set, as one type of gearteeth will be finished with a very slight reing to which the invention can be applied,

consistingofa pinion 10 and a ring gear 11.

The invention applies equally well to other types of gear sets, however 1t applies-more particularly to gear sets formed of hardened metal such as steel. The pinion illustrated has fewer teeth than the ring gear with which it is to mesh when finished, and while the invention applies particularly to gear sets in which the gears have different numbers of teeth, still it can be utilized to an advantage when the gear teeth are the same in number.

the meshing gear teeth without grinding the same, and as a result the grinding efliciency 1s so (poor that-a relatively long time is require 7 gear teeth faces. When the pinion has fewer teeth than the ring gear, the faces of its teeth willbe lapped much faster than the faces of the ring gear teeth and this is .an undesirable in properly lapping the hardened steel condition. With hypoid gearing there is a rolling and sliding action of the meshing teeth relatively and the lapping of the faces of the inion teeth is not uniform throughout them-length with the present methods.

In carrying out my invention, I coat .one of the gears of the set with a relatively soft metal covering 12, such as copper. The

copper ispreferably applied to. the gear by an electro-plating process, so that it can later be stripped through a reversal of the current in the same bath, andthus the covering can be quickly applied and removed. After coat- ,ing one of the gears, and preferably the gearof the set having the least number of teeth,

the set is then driven in mesh. by suitable equipment and afluidabrasive is intermittently applied between the copper coated pmion teeth and the ring gear teeth. After lapping the gear set in this manner a relawith copper would be eliminated.

When the gears of the set have the same number of teeth, one gear could be plated for the first lapping operation and then strip ed while the other (gear of the set could be p ated for the secon lapping operatlon and then stripped. Such method of lappigng would save considerable time compared to the methods now employed.

By coating the gears with copper, the abrasive substance in the lapping fluid will be come imbedded in the copper covering the gear teeth faces and in such fixed relation will have a definite grinding eflectjupon the faces of the teeth of the other gear whilemeshing therewith, and thus the faces are lapped in a very materially shorter time than that required when the abrasive substance is substantially unrestricted to roll or be pushed ahead of the abutting faces of the teeth as they mesh.

The relapping operation need beonly sufficiently long to take the high spots ofi of the faces of the pinion teeth. I have found that the copper coating need to be only..002 inch in thickness to serve as the base for securing the abrasive during the lapping operation.

While I have herein described in some detail'a specific embodiment of my invention,

' which I deem to be new and advantageous and may specifically claim, I do not desire it to be understood that my invention is limited to the exact details of the construction,

as it will be apparent that changes may be made therein without departing from the s irit or scope of my invention.

fivhat I claim is:

1. The method of lapping gear sets compnsmg coating one of the gears with a relatively soft metal, running the gears in mesh, applying a grinding compound between the teeth of the coated gear and the other gear,

stripping the coating from the gear, again runnmg the gears together uncoated, and applying a grinding compound between the teeth while the uncoated gears are running together.

2. The method of lapping gear sets comprising coating one of the gears with copper, running the gears together with one "coated, applying a fluid grinding compound to the gear teeth while running, stripping the copper from the gear, running the gears together uncoated, and applying a fluid grindapplyin a fluid grinding compound to such unplate gears while they are running to gether.

4. The method of grinding one gear of a gear set comprising coating another gear with an abrasive retainlng material, runnin the gears together with the one coated, an applying an abrasive material to the gear teeth durin rotation together.

5. he method of lapping the teeth of a reduction drive gear set comprisin plating the gear with the least teeth wit copper, runnin the gear, set together with the one gear 5) ated, applying a fluid abrasive compoun to the gear teeth while running together, strippin the copper from the gear, again running t e gear set, and applying a fluid abrasive compound to the gear teeth while again running to ether.

In testimony whereof afiix my si ature.

JOHN M. CHRIST N. 

